Summary Currently, ~15% of couples worldwide and ~12% of men in the United States are subfertile or infertile. Some root causes for this infertility lie in genetic defects, but others are due to exposure to industrial and environmental toxicants, injury, or medical treatments such as alkylating chemotherapies which almost always result in sterility, especially in men. Male pre-pubertal cancer patients are especially at risk since they are unable to provide a semen sample prior to their cancer treatments. Fertility preservation in pre-pubertal pediatric cancer patients is an emerging and ever-evolving field. However treatment options are limited. Since 1980, Assisted Reproductive Technology (ART) has gained worldwide acceptance and Intracytoplasmic Sperm Injection (ICSI) has since aided couples with severe infertility to achieve pregnancies. However, these advanced techniques require the production of even a small amount of functional gametes. For those individuals rendered sterile by non-genetic root causes unable to produce gametes, such as pediatric cancer survivors, there are no cures for their infertility. As the incidences of pediatric cancers, including testicular and germ cell cancers, continue to rise, there is a need for the development of novel stem-cell based therapies to treat male factor infertility in patients rendered sterile by medical treatments. Patient-specific pluripotent stem cells represent one future potential source to restore fertility by generating germline precursors such as spermatogonial stem cells (SSCs) in vitro that can restore fertility in vivo following transplantation. This therapeutic approach would allow infertile men to produce offspring with their partners without having to use advanced reproductive technologies such as ICSI. Our team has pioneered the ability to transplant autologous and donor rhesus SSCs into recipient rhesus testes to re- colonize the testis and restore fertility. Additionally, our group was the first group to derive SSC-like cells from human induced pluripotent stem cells (iPSCs). Here, we hypothesize that NHP iPSC-derived SSCs can be transplanted into sterilized autologous recipient testes to restore fertility. Furthermore, we hypothesize that sperm generated from transplanted recipients can produce healthy embryos and offspring. This proposal under PAR- 16-093 Improvement of Animal Models for Stem Cell-based Regenerative Medicine (R01) will determine, using a non-human primate stem cell model, whether iPSCs can be utilized to treat male factor infertility.